Metal analyzing plasma CNC cutting machine and associated methods

ABSTRACT

A plasma computer numerically controlled (CNC) cutting machine is controlled by a computers. In an embodiment, the computer executes a CNC program to control movement of a plasma torch to cut parts from a workpiece while a spectrometer determines emissions spectra of light emitted in a brief time window as the torch begins to cut the workpiece. The spectrometer cooperates with the computer to analyze the metal as it is being cut by the CNC cutting machine and determine a composition. In embodiments, the composition is compared to an expected composition and saved in a database with identifying information; in a particular embodiment the database is queried to provide identifying information of metal having similar composition to the workpiece.

PRIORITY AND RELATED APPLICATIONS

The present application claims priority to U.S. patent application Ser.No. 15/886,806 filed 1 Feb. 2018, and for the United States is acontinuation in part of U.S. patent application Ser. No. 15/886,806.U.S. patent application Ser. No. 15/886,806 is in turn acontinuation-in-part of U.S. patent application Ser. No. 15/490,088filed 18 Apr. 2017 now expected to issue as U.S. Pat. No. 10,195,683 onFeb. 5, 2019, and a continuation-in-part of International ApplicationNo. PCT/IB2017/055215 filed 30 Aug. 2017. U.S. patent application Ser.No. 15/490,088 and International Application No. PCT/IB2017/055215 claimpriority to U.S. Provisional Patent Application No. 62/421,919, filed 14Nov. 2016. The entire contents of the aforementioned applications areincorporated herein by reference.

FIELD OF THE INVENTION

This invention pertains to plasma metal cutting using a numericallycontrolled machine and spectral analysis to determine metallurgicalcomposition of metal.

BACKGROUND

When purchasing steel from multiple sources, quality of the steel maynot be as dependable and as stable as when purchasing steel from asingle source. Also, some steel has unusual composition such as alloyingcomponents like Boron, which reduces import duty but affects thebehavior of the metal and requires different welding. When this chemicalcomposition becomes hidden in the steel supply chain, the steel can bedangerous.

Originally, only chemical analysis could determine metallurgicalcomponents of the steel, and specialty steel suppliers employedmetallurgists with laboratory equipment to test the steel. With therapid availability of high performance microcomputers, heavy stand-alonemachines use an arc for spectrographic analysis of a metal sample. Newertest equipment uses Energy Dispersive X-ray Fluorescence (ED-XRF)technology for spectral analysis of steel, although they are expensiveand not practical for steel processing workshops.

Plasma cutters have become common for metalworking, including workingwith steel, aluminum, and other metals. In plasma cutting, a plasmaformed of a gas heated by an electric arc serves to conduct electricityinto, and remove melted metal from, a metal workpiece. Plasma cuttersmay be used with “numerically controlled” (NC), computer controlledcutting machines, or may be handheld.

SUMMARY

A plasma computer numerically controlled (CNC) cutting machine iscontrolled by a computer such as a personal computer capable running anoperating system and software programs. In an embodiment, the computerexecutes a CNC program to control movement of a plasma torch to cutparts from a workpiece while a spectrometer determines emissions spectraof light emitted as the torch cuts the workpiece. The spectrometercooperates with software running on a computer to analyze the metal asit is being cut by the CNC cutting machine and determine a composition.In embodiments, the composition is compared to an expected compositionand saved in a database with identifying information; in a particularembodiment the database is queried to provide identifying information ofmetal having similar composition to the workpiece

In an embodiment, a method for analyzing composition of a workpiecebeing cut by a plasma CNC cutting machine, includes capturing light froma plasma arc of the plasma CNC cutting machine as the plasma arc cuts apart from the workpiece; generating spectral data from the light; andprocessing the spectral data to generate a determined compositionindicative of composition of the workpiece.

In another embodiment, a plasma CNC cutting machine of the type having abed for supporting a workpiece to be cut, a gantry that traverses thebed, a plasma cutting head apparatus mounted to the gantry, and acomputer having a processor and memory storing CNC control softwarehaving instructions executable by the processor to control the gantryand the plasma cutting head apparatus to cut the workpiece with a plasmaarc, has improvements including a lens positioned and configured tocapture light from the plasma arc and direct the light through anoptical path; a spectrometer configured to analyze light receivedthrough the optical path and generate spectral data therefrom; andspectral analysis software comprising machine readable instructionsstored in the memory and executable by the processor to analyze thespectral data and generate a determined composition indicative ofcomposition of the workpiece.

In yet another embodiment, a metal analyzing plasma CNC cutting machine,includes a plasma cutting torch controllable to cut a workpiece with aplasma arc; a lens positioned and configured to capture light from theplasma arc; a spectrometer coupled to receive light from the lensthrough an optical fiber path and adapted to determine spectral data ofthe light; at least one computer having a processor and memory storingspectral analysis software that includes machine readable instructionsexecutable by the processor to analyze the spectral data and generate adetermined composition indicative of a composition of the workpiece.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows one example of a metal analyzing plasma CNC cuttingmachine, in an embodiment.

FIG. 1A shows a collimator of an embodiment, the collimator used tonarrow light collection to light emitted at specific points of theplasma arc and workpiece.

FIG. 2 shows the bevel head of the plasma CNC cutting machine of FIG. 1in further detail showing a spectral analyzer optically coupled to alens positioned proximate plasma arc, in an embodiment.

FIG. 3 shows the computer of FIG. 1 in further example detail, in anembodiment.

FIG. 4 is a spectral graph illustrating example spectral data capturedover the range 250 to 600 nanometers by the metal analyzing plasma CNCcutting machine of FIG. 1 when cutting the workpiece, in an embodiment.

FIG. 4A is a spectral graph captured over the range 290 to 400nanometers in a one-thirtieth second window as cutting begins.

FIG. 4B is a spectral graph captured over the range 290 to 400nanometers (0.1 nm resolution) captured later in the cutting processthan the spectral graph of FIG. 4A.

FIG. 4C is a spectral graph captured over the range 290 to 400nanometers (0.1 nm resolution) captured during the one-thirtieth secondwindow while cutting a stainless steel.

FIG. 5 is a flowchart illustrating one example method for analyzingmetal using the metal analyzing plasma CNC cutting machine of FIG. 1, inan embodiment.

FIG. 6 is a spectral graph illustrating broadband spectral data capturedover the range 270 to 1050 nanometers by a metal analyzing CNC cuttingmachine when the workpiece is first penetrated, showing offsets fromblack-body radiation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows an example metal analyzing plasma CNC cutting machine 100.Like conventional plasma cutting machines, machine 100 includes a bed140, a gantry 150, and a head apparatus 125 that holds and manipulates aplasma torch 120. A computer 135 (e.g., a personal computer capablerunning an operating system and software programs) communicates with aremote amplifier box 137 that generates signals through cable 130 forcontrolling servo motors of gantry 150, head apparatus 125, and plasmatorch 120. A metallic workpiece 110 to be cut by machine 100 is placedon bed 140. In the example of FIG. 1, workpiece 110 is a steel gratingbut may represent any metallic material that may be cut by machine 100such as steel, aluminum, or brass sheet or plate up to six inches thick.

In certain embodiments, head apparatus 125 may be a bevel head apparatussuch as can be found in U.S. Pat. No. 8,865,056, which is includedherein by reference for purpose of enablement. Bevel head apparatus 125holds, swivels and tilts torch 120 up to 57 degrees in any plane. Bevelhead apparatus 125 includes a pantograph arm 127 that is mounted to anactuator box 128 that contains motors and drivers that manipulate thepantograph arm and plasma torch 120 to cut workpiece 110. Actuator box128 is formed of metal and acts as a ‘Faraday cage’ to shieldelectronics included therein from radiation and heat generated by theplasma arc. Box 128 may be cooled in some embodiments, such as by fans.

In a particular embodiment, plasma torch 120 is initiated by 5,000 voltsat a frequency of 2 MHz that ionizes gas released in a high-pressurestream to form a plasma arc with a temperature of around 10,000 C. Thisplasma arc draws a DC current of between 10 amps and 1200 amps at around150 volts once established. The power released by the plasma arc mayreach 180 kW and is typically around 37 kW, and is sufficient to meltthick steel quickly using only electricity and air (although other gasmixes may be used). The plasma arc and melting steel is hot and emitslight that carries a wealth of spectral information about the steelbeing cut, particularly in the electromagnetic spectrum range of UltraViolet (UV) light.

The plasma arc creates a difficult environment for electronic devices,as it is very hot, splatters molten metal, and its arc-formation powersupply of 5,000 volts at a frequency of 2 MHz, generates considerableelectromagnetic radiation that interferes with nearby electronicdevices. It is therefore difficult to position sensitive electronicequipment near plasma torch 120.

A fiber optic cable allows the sensing electronics to be safely isolatedinside a metal Faraday cage while continuously collecting light from theplasma arc. The Faraday cage shields the sensing electronics from theelectromagnetic radiation (radio interference) and heat generated by theplasma arc.

Thus, by combining the spectral analyzer, coupled by the fiber optic tothe plasma CNC cutting machine, emissions spectra from the metallurgiccomponents of the steel being cut may be monitored periodically orcontinuously, and those emissions spectra analyzed to determinemetallurgic components of the steel being cut. This analysis is like theanalysis done for spark analysis which also uses an electric arc togenerate light to determine a composition of a metal sample. However,the advantages of machine 100 include that the analysis takes noadditional time or effort beyond that needed to cut the workpiece 110.

Pantograph arm 127 is modified to include a lens 182, positioned tocapture electromagnetic radiation, particularly in the ultraviolet lightportion of the spectrum, from the plasma arc formed by plasma torch 120while the plasma arc is cutting workpiece 110. For example, lens 182 hasa focal length based upon its position relative to the plasma arc, tocapture light (i.e., at least a portion of the electromagnetic spectrum)generated by the plasma arc. An optical path 184, which may be a singlestrand or a multiple-strand fiber optic cable, optically couples lens182 to a spectrometer 180 positioned within box 128. Thus, spectrometer180 is protected from interference from the plasma arc but receiveslight emitted from the plasma arc, via lens 182 and optical path 184,while cutting workpiece 110. Spectrometer 180 is selected based upon thespectral ranges of light produced by the plasma arc of the cutting torchas known in the art of spectral analysis. In one example, spectrometer180 is a Blue-Wave Miniature Fiber Optic Spectrometer device fromStellarNet Inc., however, other spectrometer devices may be used withoutdeparting from the scope hereof.

In a particular embodiment, lens 182 is mounted at the rear of acollimator constructed of a ten-centimeter-long aiming tube 190 (FIG.1A) of diameter one centimeter. The collimator is adapted to be aimed atparticular portions of the plasma arc to avoid undue interference fromlight emitted as black-body radiation by nearby hot metal—it is believedthat the collimator should be aimed to optimize collection of light fromplasma adjacent the workpiece being cut as cutting begins and metalvapor first explodes from the workpiece into the arc, and not aimeddirectly at either the workpiece or the electrodes that form the arc.Use of the collimator permits collecting light from particular portionsof the plasma arc despite placement of the lens 182 and optical path 184at a sufficient distance from the plasma arc to prevent damage to lens182 and optical path 184 that may otherwise be caused by the intense arcthat in some embodiments reaches or exceeds 40 kw. In a particularembodiment, a black rubber cork 191 having a drilled hole 192 is fittedat an end of the tube 190 distal to lens 182 and optical fiber oroptical path 184 to narrow a field of view of the collimator. The lensfocuses light that has passed through the drilled cork and tube onto anend of optical path 184, which in an embodiment is an optical fibercapable of transmission from 190 to 2200 nanometers. In an alternativeembodiment a telescopic collimator is used to collect light from theplasma arc into the optical path.

Spectrometer 180 is communicatively coupled to computer 135 via acommunication cable 186, such as an electrically screened cable or afiber-optic communications cable. Spectrometer 180 may share acommunication path between bevel head apparatus 125 and computer 135without departing from the scope hereof. In one particular embodiment,communication cable 186 is a USB cable. Computer 135 includes software188 that processes data received from spectrometer 180 to determinemetallurgical content of workpiece 110 based upon a spectrum captured byspectrometer 180 while workpiece 110 is being cut by machine 100.

FIG. 2 shows bevel head apparatus 125 of metal analyzing plasma CNCcutting machine 100 of FIG. 1 in further exemplary detail. Lens 182 ispositioned on a lower armature 230 of pantograph arm 127 in alignment238 with a plasma arc 210 formed by plasma torch 120. As such, theposition of lens 182 relative to the plasma arc 210 is constant, since,due to the advantages of the pantograph design, the center of plasma arc210 does not move relative to lower armature 230. Further, as plasmatorch 120 is moved to cut workpiece 110, lens 182 remains in a constantposition relative to plasma arc 210. That is, lens 182 is positioned onthe arm supporting plasma torch 120 and moves with the torch. When otherforms of cutting head are used instead of bevel head apparatus 125, lens182 is similarly positioned to ensure that lens 182 is aligned withplasma arc 210, and remains near the plasma arc to capture light fromthe plasma arc while excluding most surrounding ambient light, and movesas the plasma arc moves to cut workpiece 110. For example, as bevel headapparatus 125 moves up and down relative to a backplane 250, which inturn moves left and right relative to gantry 150, which in turn movesbackwards and forwards relative to bed 140, lens 182 remains alignedwith, and near, plasma arc 210.

Optical path 184 conveys the light captured by lens 182 to spectrometer180 that spectrally analyzes the light to generate spectral data 181.Spectral data 181 is for example a digital representation of spectralcontent of the light captured by lens 182 from plasma arc 210. Lens 182moves together with bevel head apparatus 125 as torch 120 is controlledto cut workpiece 110 and spectrometer 180 is positioned a safe distancefrom plasma arc 210 and couples via optical path 184.

As shown in FIG. 2, lens 182 is positioned at a distal end of lowerarmature 230 to capture at least part of the electromagnetic spectrumgenerated by plasma arc 210 as it cuts workpiece 110. Lens 182 mayinclude a front element or window that is replaceable in the event ofdamage caused by plasma arc 210 or splattered molten metal. Optical path184 may be positioned within lower armature 230 for protection fromdamage by plasma arc 210 and is for example a flexible fiber opticalcable that conveys light from lens 182 to spectrometer 180. In analternative embodiment, optical path 184 lies within a tubular conduitto protect it from damage. Spectrometer 180 is for example a microspectrometer that uses a diffraction grating and sensing array to derivespectral data 181 from the light received via optical path 184, thespectral data includes an intensity and wavelength (or equivalentlyfrequency) distribution of light generated by plasma arc 210. Spectraldata 181 is sent to computer 135 for further analysis.

FIG. 3 shows computer 135 in further example detail. Computer 135includes at least one processor 302 communicatively coupled to memory304. Memory 304 is non-transitory and represents one or both of volatilememory (e.g., RAM, SRAM, DRAM, and so on) and nonvolatile memory (e.g.,ROM, PROM, EPROM, FLASH, magnetic media and optical media). Memory 304is shown storing software 188 that includes an operating system 310, aCNC controller 320 function, and a spectral analyzer 330 routine.Operating system 310 provides a real-time multitasking environmentwithin computer 135 for concurrently executing CNC controller 320 andspectral analyzer 330. Operating system 310 is selected from the groupincluding Microsoft® Windows™, Apple® OS™, and so on. For example,operating system 310 coordinates execution of CNC controller 320 andspectral analyzer 330.

CNC controller 320 follows a CNC program 322 to control movement andoperation of plasma torch 120 to cut parts from workpiece 110 asdesired. For example, CNC controller 320 may send commands, via CNCcontrol interface 324 and remote amplifier box 137, to each of gantry150, bevel head apparatus 125 and plasma torch 120. As known in the artof CNC controllers, CNC controller 320, gantry 150, and bed 140 areconfigured so that CNC controller 320 can direct movement of gantry 150along bed 140, and of bevel head apparatus 125 along gantry 150, therebypermitting CNC controller 320 to move bevel head apparatus 125 toposition plasma torch 120 at any X-Y coordinate in a predefinedoperational area lying within a plane over and parallel to bed 140.Similarly, CNC controller 320 is configured to control motors within box128 to operate pantograph arm 127 to position plasma torch 120 at any Zor height coordinate within a predefined operational volumeincorporating the plane over and parallel to bed 140. CNC controller isthereby configured to position torch 120 at any position within thepredefined operational volume as needed to make preprogrammed cuts toworkpiece 110.

Operating system 310 runs spectral analyzer 330 concurrently with CNCcontroller 320 to process spectral data 181, received via interface 308and communication cable 186 from spectrometer 180, and generatedetermined composition 334. CNC controller 320 and spectral analyzer 330may communicate such that spectral analyzer 330 controls spectrometer180 to capture spectral data 181 only when plasma torch 120 is activeand plasma arc 210 is present.

In one example of operation, CNC controller 320 and spectral analyzer330 cooperate to capture spectral data 181, the spectral data includingemissions spectra information, from different areas of cut of workpiece110 as it is cut by machine 100, and spectral analyzer 330 generatesdetermined compositions 334 for each different area of cut.

For purposes of this document, a composition of a metal workpiece, suchas workpiece 110, is a list of elements that may be found in metalworkpieces together with a percentage of each element of the list thatis present in the workpiece. For example, metal workpieces of cast iron,steel, aluminum, brass, bronze, or copper may contain aluminum, arsenic,beryllium, bismuth, boron, carbon, cerium, chromium, copper, iron, lead,magnesium, manganese, molybdenum, nickel, phosphorous, silicon, silver,sulfur, tin, titanium, tungsten, vanadium, zinc, and zirconium atvarious percentages. It is well known that percentages of each elementpresent in a metal workpiece may dramatically affect physical propertiessuch as hardness of the workpiece, as well as chemical properties likecorrosion resistance, for example hardness of steel is significantlyaffected by carbon percentage content, and corrosion resistance bychromium, and nickel percentage content. Similarly, copper-based alloyshave physical properties that are significantly affected by tin, zinc,and aluminum percentages. Generally, emissions spectra of each elementin isolation are known. Emissions spectral data 181 includes asuperposition of emissions spectra of the elements included in acomposition of workpiece 110.

Trace elements such as europium and iridium may also be present, andproduce characteristic spectral lines in the emissions spectral data.Trace elements typically have concentrations low enough to notsignificantly affect physical properties of the workpiece, but theseconcentrations are of interest in fingerprinting the steel to identifysources.

Various bodies, including the Society of Automotive Engineers (SAE) andASTM International, have published named specifications for metal, suchas SAE grade 440 steel, ASTM A1 for railroad rails, ASTM A182 forstainless steel pipe fittings, A354 for steel alloy bolts, and A514 forweldable steel plate; each specification includes a range of allowablepercentages of specific elements for composition of metal acceptableunder the specification as well as other factors, such as heattreatments, used in producing metal objects to meet the specification.Other specifications, such as for rifle barrels, armor plate and bolts,screws, and sheetmetal used in aircraft construction, have beenpublished by governmental and military agencies. These specificationsmay be referenced by those who order metal from foundries.

In each specification, some elements are regarded as desired, mandatory,alloy constituents, such as iron and carbon in steel, typically addedintentionally when workpieces are made at a foundry and for whichassociated percentages appear in specifications as ranges with non-zerominimum and maximum values. Other elements, such as excessive boron orsulfur in steel, may be regarded as objectionable impurities, with onlya maximum listed for some specifications, but are sometimes present inworkpieces. Still other elements, such as rare earth elements oractinide series elements, may be present in trace amounts, theirpercentages in composition of workpieces is useful in fingerprintingworkpieces and tracing origin to particular mines and mills even thoughthey may not be listed in common specifications and may be atsufficiently low concentrations that they do not significantly altermaterial properties of the workpiece.

Spectral analyzer 330 includes include machine readable instructionsthat, when executed, perform methods known in the art for identifyingpeaks in spectral data 181 and fit known emissions spectra of eachelement of a composition of workpiece 110 to observed emissions spectra,thereby identifying percentages of each element in workpiece 110 anddetermining determined composition 334 of workpiece 110. Whilepercentages of most elements in workpiece 110 can be identified usingair as the gas from which the plasma is formed, in some embodiments aninert gas such as argon is used as the supplied gas so that percentagesof oxygen and nitrogen in the workpiece 110 can be determined duringcutting.

In some embodiments, an expected composition 352 of workpiece 110 isdefined prior to cutting of workpiece 110. In embodiments, expectedcomposition 352 includes ranges of acceptable content for particularelements. In a particular embodiment, this desired composition isentered into computer 135 as expected composition 352. In an alternativeembodiment, a specification identifier is entered into computer 135,whereupon computer 135 queries a database 139 on a server 136, whichreturns expected composition ranges from a specification entry 141 ofdatabase 139 to computer 135 as expected composition 352. In eitherembodiment, once cutting of workpiece 110 by machine 100 starts,spectral analyzer 330 determines determined composition 334 from lightof plasma arc 210, and compares the determined composition 334 toexpected composition 352, generating an alert 354 when determinedcomposition 334 indicates that workpiece 110 is not of the expectedcomposition 352. For example, spectral analyzer 330 and computer 135 maybe configured to ignore variations in composition that are within limitsof a specification or to ignore other minor variations in composition,and/or may be configured to generate alert 354 when unwantedcontaminants are identified in workpiece 110 or determined compositionlies outside limits of a specific specification.

Computer 135 may also include a user interface 350 for interacting withan operator of machine 100, and user interface 350 may display one orboth of determined composition 334 and alerts 354 to the operator asmachine 100 cuts workpiece 110.

In an embodiment, computer 135 is coupled through a computer network138, which in a particular embodiment is a local network and in anotherparticular embodiment is the Internet, to server 136 having steelcomposition information in database 139.

In embodiments having database 139, database 139 may be configured withspecification entries 141 for each of several specifications of metal,such as steel, with composition ranges for each specification. In aparticular embodiment, database 139 is configured with a table ofacceptable compositions, typically entered as ranges of percentages foreach of several elements, indexed by published specificationidentifiers.

In embodiments having database 139, database 139 may also be configuredwith composition database entries 143 having determined compositions, orfingerprints, for metal of each of several specifications as produced byeach of several foundries. These determined compositions may be measuredby plasma cutting machines herein described, or determined byspectrometric analysis with other equipment. In embodiments havingcomposition database entries 143, computer 135 is configured to upload adetermined composition 334 of each workpiece 110 to database 139 as anadditional composition database entry 143 with any identifiedspecification and identification of the foundry or steel mill theworkpiece originated from.

It is known that iron ore varies in composition from mine to mine, andthat impurities found in ore may appear in smelted metal. For example,iron ore from the Dannemora mine in Sweden was low in phosphorus andsulfur, while high in certain other metals; during the seventeenth andeighteenth centuries cast iron cannon made from Dannemora ore developeda reputation as being much less likely to explode when fired than cannonmade from iron ore from many other sources because of the ore's lowsulfur and phosphorous content. While major impurities and amounts ofalloying elements, including sulfur and phosphorous, are often correctedduring modern smelting and foundry operations, other, minor, alloyingelements and impurities may not be corrected and will show as minorelements in determined composition 334. Typically, major impurities andalloying elements are associated with a specification of metal inworkpiece 11, while minor elements in workpiece 110 are associated witha source from which the workpiece originated. The pattern of theseimpurities in determined compositions in database 139 can thereforeserve to help identify a source for the workpiece.

In an embodiment, after determining determined composition 334, computer135 and server 136 are configured to search database 139 for compositiondatabase entries 143 most closely matching in major alloying elements todetermined composition 334 and provide identifying information to a userregarding specifications associated with those nearest compositionentries. Further, computer 135 and server 136 are configured to searchdatabase 139 for composition database entries 143 most closely matchingin minor elements to determined composition 334 and provide afingerprint identifying information to a user regarding a likely sourceof metal in workpiece 110. For example, for a stainless-steel workpiece,iron, nickel and chromium are major alloying elements added withpercentages greater than one percent during foundry operations and areindicative of a specification for the stainless steel, while certainother elements of determined composition 334 are typically notintentionally added and their concentrations are part of the fingerprintfor identifying a source of the metal in workpiece 110.

FIG. 4 shows one example spectral data 181 from 250 to 600 nanometerscaptured after metal is pierced by metal analyzing plasma CNC cuttingmachine 100 of FIG. 1 when cutting workpiece 110. In this example,workpiece 110 is stainless steel and contains molybdenum and spectraldata 181 shows multiple of spectral features 402. Determined composition334 may be generated from spectral data 181 near instantly as spectraldata 181 is sent to computer 135 as machine 100 cuts workpiece 110.Determined composition 334 shows the constituent elements of workpiece110 in proportion. For steel, a major constituent is Iron (Fe), but itmay include other constituents such as Chromium for stainless, Carbon,Molybdenum, Vanadium, Titanium, and Boron, and may also includeimpurities such as Sulfur and other elements. By providing machine 100with simultaneous cutting and spectral analysis capability, the operatormay verify that workpiece 110 is of correct composition and is warned ofunwanted impurities or unexpected presence of critical alloying elementssuch as Boron. Being aware of unexpected composition at the first cut ofworkpiece 110 saves potentially wasted time in cutting and attempting toweld steel contaminated with Boron, for example. Spectral analysis ofeach workpiece also prevents unexpected reduction in finished itemquality.

FIG. 5 is a flowchart illustrating one example method 500 for analyzingmetal using metal analyzing plasma CNC cutting machine 100 of FIG. 1.Method 500 is implemented by lens 182, optical path 184, spectrometer180, and computer 135 of machine 100. In this example, method 500 startswhen machine 100 is about to cut, or has started cutting workpiece 110.If not already entered, a specification or desired composition ofmaterial of the workpiece is optionally entered 501 into computer 135.If a specification name is entered, in step 503, computer 135 isconfigured to access a corresponding specification entry 141 in database139 of server 136 and fetch an expected composition database entry 143from database 139 into local expected composition 352.

Step 502 is a decision. If, in step 502, method 500 determines that thearc has been ignited, method 500 continues with step 504; otherwise,method 500 continues with step 518. In one example of step 502, spectralanalyzer 330 cooperates with CNC controller 320 to determine whetherplasma arc 210 is operating on plasma torch 120. In another example ofstep 502, spectral analyzer 330 processes spectral data 181 to determinewhen plasma arc 210 is operating.

In step 504, method 500 captures light from the plasma arc. In oneexample of step 504, lens 182 captures light from plasma arc 210 andoptical path 184 conveys the light to spectrometer 180. In step 506,method 500 generates spectral data from the light. In one example ofstep 506, spectrometer 180 generates, using a diffraction grating andsensors, spectral data 181 from light captured by lens 182.

It has been found that during normal cutting, there is much interferencefrom the intense light of the plasma arc, including spectral lines fromcopper, silver, and hafnium eroded from the anode and cup electrodesbetween which the plasma arc extends. Further, spectral lines at longwavelengths become heavily obscured by black-body radiation from hotmetal as the metal being cut is heated by the plasma.

Spectral analysis of black-body radiation from metal being cut asindicates temperatures on the order of 3500 degrees Celsius, whiletemperatures of the plasma itself may reach 10,000 degrees Celsius.Broad-wavelength spectra, as illustrated in FIG. 6 over the range of 270to 1050 nanometers, and spectra captured during normal cutting conveylittle information about the metal being cut. In the spectra of FIG. 6,the broad base curve 602 underlying the spectra is produced byblack-body radiation.

The best spectra obtained from the light of the plasma arc are in thewavelength range from 290 to 400 nanometers, as illustrated in FIG. 4A.Further, to avoid interference from black-body radiation, spectra mustbe captured in a brief time window as the arc is established and cuttingbegins; after sufficient metal is ionized and excited to providespectral emissions lines, but before these spectral lines are drowned ina combination of spectral lines emitted by ions from eroded cap andanode electrodes and intense black-body (Stefan Boltzmann) radiationfrom the hot metal being cut.

In an embodiment, spectra over the wavelength range 290-400 nanometerswith resolution 0.1 nanometer or better, as illustrated in FIG. 4A, arecaptured in a time window of one-thirtieth second as cutting begins assparks explode from the workpiece being cut into the plasma as theworkpiece is first penetrated. In a particular embodiment for cuttingsteel, a sequence of spectra is captured in narrow windows ofone-thirtieth second at a rate of thirty spectra per second as cuttingbegins, each spectrum is examined for presence of a 347.6 nanometerspectral line emitted by ionized iron, a number of the first spectracontaining this iron emissions line as cutting begins are captured and aratio of intensity of the iron line to background light is determined.The best of these captured spectra, as indicated by the ratio of ironemissions line intensity to background, is processed to identify boththe primary steel alloy constituents and the secondary impurities of thesteel.

In an alternative embodiment, the sequence of spectra is captured inwindows of width one-sixtieth of a second at sixty spectra per second ascutting begins. In other alternative embodiments the narrow time windowfor capturing each spectra of the sequence of spectra is of other timedurations less than or equal to one thirtieth of a second, and with acorresponding frame rate.

In the spectra of FIG. 4A, captured as cutting begins, spectral lines ofchromium 405, copper 407, and other elements are recognizable.Experiment shows that spectra acquired even one tenth of a second beforeor after the best captured spectra lack sufficient detail for analysis.

In an alternative embodiment, adapted for cutting aluminum workpieces,instead of examining each spectra for an iron line, each spectra isexamined for presence of an aluminum emissions line and a ratio ofintensity of the aluminum emissions line to background light is used toidentify the best of captured spectra. The identified best of capturedspectra is used to determine both the primary alloy constituents andsecondary impurities of the aluminum workpiece.

FIG. 4B is a spectral graph captured over the range 290 to 400nanometers (0.1 nm resolution) captured a second later in the cuttingprocess than the spectral graph of FIG. 4A. and illustrative of theinterference from black-body radiation background light that tends toobscure spectral peaks during most of the cutting process.

FIG. 4C is a spectral graph captured over the range 290 to 400nanometers captured during the one-thirtieth second window as cutting astainless steel workpiece begins. The three highest peaks 408 representchromium, an element found in far higher concentrations in moststainless steel than in low-carbon non-stainless steel, and permit thesystem to distinguish stainless from low-carbon non-stainless steel.

In step 507 each spectra is examined for presence of a 347.6 nanometerspectral line emitted by ionized iron. Step 509 is a decision, if ironis not found, the system retries capturing 504 the spectra. A smallnumber of the first spectra containing this iron line are processedfurther in step 508.

In step 508, method 500 processes the spectral data and generates adetermined composition. In one example of step 508, spectral analyzer330 is executed by processor 302 to process spectral data 181 andgenerate determined composition 334.

Step 510 is optional. If included, in step 510, method 500 displays thedetermined composition of step 508 to an operator. In one example ofstep 510, spectral analyzer 330 displays determined composition 334 onuser interface 350 of computer 135.

Step 511 is optional. If included, in step 511, method 500 logs thedetermined composition as an entry in the database. In one example ofstep 511, spectral analyzer 330 logs determined composition 334 asspecification entry 141 of database 139.

Steps 512 through 516 are also collectively optional. If included, instep 512, method 500 compares the determined composition 334 to anexpected composition 352 of the workpiece. Step 514 is a decision. If,in step 514, method 500 determines that the determined composition andthe expected composition match to within limits, method 500 continueswith step 518; otherwise, method 500 continues with step 516.

In step 516, method 500 generates an alert indicating unexpectedcomposition. In one example of step 516, spectral analyzer 330 generatesalert 354 and displays alert 354 on user interface 350. Method 500 thencontinues with step 517.

Steps 517 and 519 are optional. In step 517, method 500 inspectscomposition database entries 143 to determine a closest match of thedetermined composition 334 to determined composition portions ofpre-existing database entries, first for major constituents to identifya specification of metal in the workpiece, and second for minorconstituents to identify a source mill or foundry from which the metaloriginated. Then, in step 519, method 500 displays information, such asa SAE or ASTM specification name, and/or a foundry name, regarding thedatabase entries that have the closest matches to the determinedcomposition 334. In an alternative embodiment, method 500 displays basicinformation about the alloy, classifying the alloy in broad categoriessuch as stainless steel, mild steel, and tool steel, together with anapproximate national origin of the steel, and a warning message ifexcessive impurities like boron are detected.

Step 518 is optional. If included, in step 518, method 500 waits. In oneexample of step 518, the wait is the predefined delay before repeatingstep 502. In another example of step 518, the wait is until plasma torch120 moves to cut a different area of workpiece 110. Method 500 thencontinues with step 502. Steps 502 through 518 thus repeat to determinecomposition of workpiece 110 using spectral analysis as workpiece 110 iscut by plasma arc 210.

By combining spectral analysis and plasma CNC cutting in a singlemachine (i.e., metal analyzing plasma CNC cutting machine 100), one ormore of the following advantages are achieved:

-   -   Spectral data is captured from the plasma arc as it cuts the        workpiece, thereby avoiding the need for creating a separate arc        or to use a laser to capture spectral data. This also avoids        additional damage to the workpiece as would be needed for a        separate test.    -   The optical fiber path allows the spectral capture device to be        positioned away from the plasma arc to reduce interference.    -   Where the CNC cutting machine uses a bevel head apparatus, the        actuator box is available to protect the spectral capture        device—no additional protective enclosure is needed.    -   In embodiments, the available processing power of the computer        used for executing the CNC program and controlling the cutting        machine is also used to analyze the spectral data and generate        the determined composition.    -   The combined solution makes valuable and often essential        spectral analysis readily available, practical, and convenient        for each cutting operation.    -   The combined solution is more cost effective than using separate        spectral analyzing devices.    -   Automatic composition checks for each workpiece may be performed        and the operator notified if the workpiece is of incorrect        composition.    -   The combined solution provides information to control quality        and prevent wrong materials from being used or supplied in a        field where two quite different types of steel can look        identical in a steel workshop.

Combinations of Features

The features herein described may appear in a variety of combinations inmetal analyzing computer-controlled plasma cutting machines. Among thosecombinations include:

A metal analyzing plasma CNC cutting machine designated A, including aplasma cutting torch controllable to cut a workpiece with a plasma arc;a lens positioned and configured to capture light from the plasma arcwithin a narrow time window as cutting begins; a spectrometer coupled toreceive the captured light from the lens through an optical fiber pathand adapted to determine spectral data of the light; and at least onecomputer having a processor and memory storing spectral analysissoftware that includes machine readable instructions executable by theprocessor to analyze the spectral data and generate a determinedcomposition indicative of a composition of the workpiece.

A metal-analyzing plasma cutting machine designated AA including themachine designated A and including a bed for supporting the workpiece asit is cut; a gantry that traverses the bed under control of the at leastone computer; and the plasma cutting torch is mounted to apparatusconfigured to traverse the gantry under control of the at least onecomputer.

A metal-analyzing plasma cutting machine designated AB including themachine designated A or AA, the spectrometer being positioned within anactuator box of the apparatus configured to traverse the gantry, theactuator box protecting the spectrometer from interference and damagecaused by the plasma arc.

A metal-analyzing plasma cutting machine designated AC including themachine designated A, AA, or AB the lens being configured to remain infixed alignment to the plasma arc despite movement of the plasma cuttingtorch over the bed under control of the at least one computer.

A metal-analyzing plasma cutting machine designated AD including themachine designated A, AA, AB, or AC the optical fiber path including afiber optic cable.

A metal-analyzing plasma cutting machine designated AE including themachine designated A, AA, AB, AC, or AD the spectral analysis softwarealso including machine readable instructions stored in the memory andexecutable by the processor to compare the determined composition to anexpected composition of the workpiece and to generate an alert on a userinterface of the at least one computer when the determined compositiondoes not match the expected composition.

A metal-analyzing plasma cutting machine designated AF including themachine designated A, AA, AB, AC, AD, or AE wherein the spectralanalysis software further includes machine readable instructionsconfigured to save the determined composition to a database on a server,and, when the expected composition of the workpiece does not match thedetermined composition, to identify a previous entry of the databasehaving a closest match to the determined composition.

A plasma CNC cutting machine designated B of the type having a bed forsupporting a workpiece to be cut, a gantry that traverses the bed, aplasma cutting head apparatus mounted to the gantry, and a computerhaving a processor and memory storing CNC control software havinginstructions executable by the processor to control the gantry and theplasma cutting head apparatus to cut the workpiece with a plasma arc,the improvement including: a lens positioned and configured to capturelight from the plasma arc and direct the light through an optical path;a spectrometer configured to analyze the light received through theoptical path within a narrow time window as a particular spectral linefirst appears and generate spectral data therefrom; and spectralanalysis software comprising machine readable instructions stored in thememory and executable by the processor to analyze the spectral data andgenerate a determined composition indicative of composition of theworkpiece.

A plasma CNC cutting machine designated BA including the plasma CNCcutting machine of designated B the lens being positioned on apantograph arm of the plasma cutting head apparatus.

A plasma CNC cutting machine designated BB including the plasma CNCcutting machine of designated B or BA, the spectrometer being positionedwithin an actuator box of the plasma cutting head apparatus, theactuator box configured to protect the spectrometer from interferenceand damage caused by the plasma arc.

A method designated C for analyzing composition of a workpiece being cutby a plasma CNC cutting machine, including: capturing light from aplasma arc of the plasma CNC cutting machine as the plasma arc firstbegins to cut the workpiece; generating spectral data from the light;and processing the spectral data to generate a determined compositionindicative of composition of the workpiece.

A method designated CA including the method designated C, furtherincluding directing the light through a lens and a fiber optic cable toa spectrometer, the spectrometer configured to perform the step ofgenerating spectral data from the light.

A method designated CB including the method designated C or CA andincluding: comparing the determined composition to an expectedcomposition of the workpiece; and when the determined composition doesnot match the expected composition to within limits, generating an alertto notify an operator of the plasma CNC cutting machine of a differencebetween the determined composition and the expected composition.

A method designated CC including the method designated CB, and includingrepeating the steps of capturing, generating, and processing tocontinually monitor composition of the workpiece as it is cut.

A method designated CD including the method designated CB, or CC andfurther including retrieving the expected composition from a databaseindexed by a specification.

A method designated CE including the method designated C, CA, CB, CC, orCD and including storing the determined composition in a database withidentifying information.

A method designated CF including the method designated CE, furtherincluding accessing the database to determine a closest compositionentry match in major alloying elements of the workpiece and determininga specification of metal in the workpiece.

A method designated CG including the method designated CE or CF andincluding accessing the database to determine a closest compositionentry match in minor elements of the workpiece and determining a likelyorigin of metal in the workpiece.

Changes may be made in the above methods and systems without departingfrom the scope hereof. For example, although machine 100 is illustratedwith a bevel head apparatus 125, other configurations for holding andmanipulating torch 120 may be used. It should thus be noted that thematter contained in the above description or shown in the accompanyingdrawings should be interpreted as illustrative and not in a limitingsense. The following claims are intended to cover all generic andspecific features described herein, as well as all statements of thescope of the present method and system, which, as a matter of language,might be said to fall therebetween.

What is claimed is:
 1. A method for analyzing composition of a workpiecebeing cut by a plasma CNC cutting machine, comprising: capturing lightfrom a plasma arc of the plasma CNC cutting machine in a brief timewindow of one thirtieth of a second in duration as the plasma arc beginsto cut the workpiece, the time window beginning after a time at thebeginning of plasma cutting when the plasma has ionized enough metalfrom the workpiece to give emissions spectra from ionized metal from theworkpiece, the time window ending before emissions spectra from theionized metal from the workpiece is drowned out by interfering spectrafrom eroded torch and black-body radiation from the workpiece;generating spectral data from the light, the spectral data includingintensity of particular spectral lines of the emissions spectra fromionized metal from the workpiece; and processing the spectral data togenerate a determined composition indicative of composition of theworkpiece; wherein the time window is determined by observing a sequenceof spectra each captured in a brief time window for presence of aparticular spectral line and determining a ratio of that particularspectral line to background light, then selecting a spectrum from thesequence of spectra for analysis according to the determined ratio ofthe particular spectral line to background light.
 2. The method of claim1 where the particular spectral line is a spectral line associated withiron.
 3. A method for analyzing composition of a workpiece being cut bya plasma CNC cutting machine, comprising: capturing light from a plasmaarc of the plasma CNC cutting machine in a sequence of time windows asthe plasma arc begins to cut the workpiece, determining a sequence ofspectra from the captured light in each time window, each spectrum inthe sequence of spectra captured in a time window of the sequence oftime windows, examining each spectra of the sequence of spectra forpresence and intensity of a particular spectral line and determining aratio of the particular spectral line to background light, and selectinga spectrum of the sequence of spectra according to the ratio of thatspectral line to background light to give a selected spectrum obtainedafter the plasma arc ionizes metal from the workpiece enough to giveemissions spectra and before emissions spectra from the ionized metalfrom the workpiece is drowned out by interfering spectra from erodedtorch and black-body radiation from the workpiece; generating spectraldata from the selected spectrum; and processing the spectral data togenerate a determined composition indicative of composition of theworkpiece.
 4. The method of claim 3 where the particular spectral lineis a spectral line associated with iron.
 5. The method of claim 3 wherethe time windows of the sequence of time windows are 1/30 second induration.
 6. The method of claim 3, further comprising: comparing thedetermined composition to an expected composition of the workpiece; andwhen the determined composition does not match the expected compositionto within limits, generating an alert to notify an operator of adifference between the determined composition and the expectedcomposition.
 7. The method of claim 6 further comprising repeating thesteps of capturing, generating, and processing to re-verify compositionof the workpiece each time cutting resumes as the workpiece is cut. 8.The method of claim 6 further comprising retrieving the expectedcomposition from a database indexed by a specification.
 9. The method ofclaim 6, further comprising storing the determined composition in adatabase with identifying information.
 10. The method of claim 6,further comprising accessing the database to determine a closestcomposition entry match in alloying elements of the workpiece anddetermining a specification of metal in the workpiece.
 11. The method ofclaim 6, further comprising accessing the database to determine aclosest composition entry match in elements of the workpiece anddetermining a likely origin of metal in the workpiece.